System for connecting a connecting device, in particular a distractor, to a bone

ABSTRACT

System for connecting a connection device to a bone with a bone pin, wherein the connection device is provided with an opening for receiving the bone pin, wherein the system comprises: —said connection device; —a guiding tube arranged to guide the bone pin from the connection device to the bone for connecting the bone pin to the bone, wherein the inner diameter of the guiding tube corresponds to the outer diameter of the bone pin and wherein the guiding tube can be slidably received in the opening, the guiding tube being slidable with respect to the connection device along an axis parallel to a longitudinal axis of the opening; —a locking device arranged to be received in the opening of the connection device and arranged to engage the bone pin for locking the bone pin with respect to the connection device, wherein the guiding tube is movable with respect to the connection device and bone pin such that the guiding tube is removable from the combination of the bone pin and the connection device and wherein the locking device is arranged to lock the bone pin after removal of the guiding tube.

The present invention relates to a system and method for connecting aconnection device to a bone with a bone pin. The invention furtherrelates to an external orthopaedic device, in particular a distractor,connecting different bones or bone parts. The invention further relatesto a method for connecting an external distractor between at least twobone parts of a patient.

In the field of trauma surgery as well as in orthopaedics, externalfixators are commonly used for treatment of complex fractures,stabilization of bony structures or joints, and in bone lengtheningprocedures. In external fixation, multiple bones or bone fragments areconnected with a frame for providing additional structure to the bones,where fixation is achieved with bone pins, which can partially or fullypenetrate the bone, providing one or more options per bone pin forattachment of an external device. More complex approaches comprise theuse of ring fixators, or Ilizarov frames, which enable fixation ofmultiple bones with bone pins or tensioned wires, such that bones arereachable from nearly any direction preferably perpendicular to thelongitudinal bone axis. For fixation of less bone parts, unilateralfixators, generally connected with multiple sets of two or three bonepins, may provide the required additional structure for a treatment.

Various frame designs provide, besides fixation, additional featureslike adjustability of the frame for reconfiguration of the fixated boneparts after fixation and without replacing the bone pins, dynamizationbetween the entry sites for stimulation of bone growth, or joint motionin case of fixation of multiple bones forming a joint. Recentdevelopment introduced externally fixated devices in treatmentstrategies for joint diseases like osteoarthritis where affected jointscan be bridged by a dedicated external fixator for application of jointdistraction.

Osteoarthritis is a degenerative joint disorder, progressive over time,characterized by cartilage damage and loss, changes in peri-articularbone, synovial inflammation, and peri-articular muscle and ligamentchanges. These tissue changes are considered causative for clinicalcharacteristics like pain, stiffness, and functional disabilities(Bijlsma J W J et al. Lancet 2011; 377: 2115-26). Knee osteoarthritis isthe most prevalent form of osteoarthritis with an increasingsocioeconomic and healthcare burden. Due to, amongst others, aging ofthe population and increase in obesity at a young age occurrence of kneeosteoarthritis is estimated to increase significantly in the forthcomingyears.

Few options are available for treatment of end-stage knee osteoarthritisand none have clearly been shown to halt or reverse tissue structuredamage. Conservative treatment focuses on minimizing functionaldisability and pain relief with anti-inflammatory treatment whenindicated (Bijlsma J W J et al. Lancet 2011; 377: 2115-26).

In case of uni-lateral tibio-femoral knee osteoarthritis, high tibialosteotomy or unilateral knee arthroplasty as well as new options likepartial medial joint unloading by subcutaneous placed devices mayprovide a temporary solution. However, these techniques are ratherinvasive. Most importantly these techniques do not serve bi-lateraltibio-femoral knee osteoarthritis.

Eventually for all these cases a total knee prosthesis is indicated, andjoint tissue is removed from the bony ends and replaced by artificialjoint components. Unfortunately, these endo-prostheses have a limitedlife span due to wear and tear of the materials. The younger thepatients (the more active they still are) the shorter the life span of aknee prosthesis. In case placed at an age below 65 years the chance forrevision surgery is high. These revision surgeries are much more complexand expensive with less good outcome.

Therefore, there is a need for joint preserving treatments, to delay thefirst total knee prosthesis and with that prevent revision surgery. Forspecifically such cases, knee joint distraction has been introduced as abi-lateral tibio-femoral joint preserving procedure. In case of failureof this treatment, the joint is uncompromised and any other treatment,including surgical intervention like hemi prosthesis, osteotomy or atotal knee prosthesis remains optional.

Knee joint distraction has quite recently been introduced as atibio-femoral joint preserving procedure and is more and more acceptedas option to postpone placement of a first prosthesis below the age of65 years. Both clinical improvement and structural tissue regenerationhave been demonstrated with clinically relevant duration. (Mastbergen SC et al Nat Rev Rheumatol. 2013; 9: 277-90). This surgical treatmentgradually separates the bony ends of a joint to a certain extent,increasing the joint space width with approximately five millimetres,for a limited period of 6-8 weeks.

Separation of the bony ends is achieved with an externally fixateddevice, connected to the bones forming the joint, with in general halfbone pins drilled through soft tissues into both bone cortices. For astable fixation bone pins are placed at multiple locations in each bone,in case of the knee at the medial and lateral side of femur and tibia.The external device is connected to these bone pins, as such forming arigid structure enabling fixation of the whole joint and enablingdistraction of the joint. Joint loads during application are primarilytransduced via the external device and the bone pins, relieving theaffected joint. In the distracted configuration, a confined axialdisplacement remains present when loaded and unloaded, still preventingfurther wear and tear of the damaged articulating surfaces with theresilience potentially stimulating the regenerating capability of thejoint.

As primary functionality, external fixators provide additional stiffnessto a bony structure. Stiffness is established by interconnecting bonyparts via bone pins to a frame with specifications that suit the chosentreatment strategy. The connection between the external frame, inparticular a connection device thereof, and the bone pins should beensured in order to have advantage of other system features. Due to thevariation in optimal position between patients and anatomical sites,establishment of the connection between the bone pins and the frameoften requires multiple actions like tightening of multiple bolts frommultiple directions, while stability of the connection is not alwaysensured. Reusability of external devices, and accompanying signs of uselike burrs and wear from the cleaning and sterilization procedures,often worsen the reliability of such connections. Since placement of abone pin requires at least one line of action for attachment to a bone,it is ensured that for every placed bone pin, a certain position andorientation provides sufficient reachability for performing otheractions like fixation of the pin to the external frame. A solution whichenables use of this ensured line of action provides a more intuitive andeasy way of working for the surgeon. Moreover, the establishedconnection can become more reliable when critical components receiveinspection previous to every usage, or even are replaced.

A problem associated with known external orthopaedic devices including asystem for connecting a connection device to the bone is therefore theheaviness and bulkiness of the existing solutions to frame the bones,because of the use of many components. Moreover, existing solutionsrequire a time consuming surgery process to place the frame optimally tothe human body, because of the use of (many) external tools forplacement and assembling various system components to a functionalstructure. A further problem associated with known connection systems isthat incorrect or non-optimal placement of bone pins may result inundesirable stress levels in the pin and in the bone structure.

Fixation of the device with half-pins into the bones of the treatedjoint requires anatomically optimal positioning at each of the bony endsof the joint of interest, such that bone pins do not intersect orinterfere with critical tissue structures like nerves and blood vessels,but also not with tendons and muscle bundles and with that reducing therisk for complications or permanent damage. Furthermore, bone pinsshould not enter the joint capsule. Additionally important bone pinsshould avoid the area where later in life a prosthesis needs to beplaced, so they should be placed at a certain distance from the jointspace. Clearly there are for all joints a limited number of preferableanatomical locations where bone pins should be placed for optimal resultwith minimal damage.

As a result of the preferred anatomically available bone pin locationsat each side of the joint and at the different sides of each bone, bonepins might need positional ‘misalignment’ with respect to mechanics ofthe external fixation frame, to obtain optimal anatomical positions ofthe bone pins. In case bone pins are positioned for fixation anddistraction of the knee joint, angular misalignment around themechanical axis of the joint results from the choice for optimalanatomical pin placement.

The interaction of the bone pins with soft tissues is therefore afurther problem associated with known external fixation devices such asexternal distractors. The pin positions and orientation are dictated bythe device, such that pins may intersect with fragile soft tissue.Moreover, axial displacement cannot be guaranteed to stay parallel withthe longitudinal axis of the tibia, which is preferred. If axialdisplacement is not parallel to the longitudinal axis of the tibia, theinterdistance of the frame and the human leg increases in the lengthdirection of the femur, which is not favourable regarding jointconfiguration, and which is making this construction uncomfortable forthe patient to wear.

It is a goal of the present invention, next to other goals, to provide asystem for connecting a connection device to a bone wherein at least oneof the above mentioned problems is solved or at least alleviated.

This goal, amongst other goals, is met by a system according to appendedclaim 1. More specifically, this goal, amongst other goals, is met by asystem for connecting a connection device to a bone with a bone pin,wherein the connection device is provided with an opening for receivingthe bone pin, wherein the system comprises:

-   -   said connection device;    -   a guiding tube arranged to guide the bone pin from the        connection device to the bone for connecting the bone pin to the        bone, wherein the inner diameter of the guiding tube corresponds        to the outer diameter of the bone pin and wherein the guiding        tube can be slidably received in the opening, the guiding tube        being slidable with respect to the connection device along an        axis parallel to a longitudinal axis of the opening;    -   a locking device arranged to be received in the opening of the        connection device and arranged to engage the bone pin for        locking the bone pin with respect to the connection device,        wherein the guiding tube is movable with respect to the        connection device and bone pin such that the guiding tube is        removable from the combination of the bone pin and the        connection device and wherein the locking device is arranged to        lock the bone pin after removal of the guiding tube.

The system for connecting a bone pin to a connection device according tothe invention allows the connection device, for instance in the form ofa connection block of an external orthopaedic device, to be used as adrilling guide such that the trajectory of the bone pin is determined bythe configuration of the connection device, in particular theorientation of the opening thereof. After proper guidance of the bonepin using the opening of the connection device, the bone pin can beefficiently locked to the connection device using a locking device whichis shaped to be received in the opening of the connecting device andwhich is arranged to lock the bone pin with respect to the connectiondevice. A simple and efficient connection system that is intuitive touse is herewith provided.

Inserting the bone pins by drilling needs protection of the soft tissuesduring drilling by a guiding tube, sometimes also referred to as acannula or sleeve, around the bone pin protecting soft tissue to beharmed by the rotating bone pin during drilling. To enable drilling of abone pin through the connection device using the guiding tube andsubsequent fixation of the bone pin after removal of the guiding tube tothe connection device, a locking device is provided. In a preferredembodiment, rotation of the guiding tube is blocked during drilling.

The invention also relates to a method for connecting a connectiondevice to a bone with a system according to invention, wherein themethod comprises the steps of:

-   -   providing a bone pin in said guiding tube in the opening of the        connection device;    -   guiding the guiding tube to the bone by sliding said guiding        tube in the opening of the connection device with respect to        said connection device, such that the guiding tube abuts the        bone;    -   inserting the bone pin into the bone;    -   removing the guiding tube from the combination of the bone pin        and the connection device after insertion of the bone pin; and    -   locking the bone pin with respect to the connection device with        said locking device after removal of the guiding tube.

The opening is arranged to slidably receive a guiding tube. This allowsadjusting the relative position of the guiding tube to be adjusted withrespect to the connection device. It is in particular preferred that thedepth of the guiding tube in the patient can be adjusted, such that theguiding tube is adjusted such that the distal end of the guiding tubeabuts the bone. This prevents damage to the tissue surrounding the boneupon drilling of the bone pin.

The connection system according to the invention is in particularsuitable to connect a bone pin in accordance with a pre-plannedtrajectory. This trajectory is defined by the orientation of the openingof the connection device. This solves or at least alleviates the problemof incorrect placement of the bone pins, resulting in undesirable stresslevels in the pin and in the bone structure, as well as on the device.The guiding tube is therefore preferably slidable in the opening alongonly the longitudinal axis of the opening. Any other relative movementis preferably prevented. The step of guiding the guiding tube thereforepreferably comprises keeping the connection device substantiallystationary with respect to the patient.

According to a preferred embodiment, the locking device has an annularbody having an outer diameter corresponding to the diameter of theopening of the connection device and an inner diameter suitable forengaging the bone pin. The outer surface having the outer diameter isthen arranged to efficiently connect to the connection device due to thematching diameters. As an alternative, or in addition thereto, it mayhowever also be possible that the locking device and the connectiondevice interconnect at another location than the outer surface of thelocking device.

The inner surface of the locking device is then arranged to be able tolock the bone pin by engagement. This prevents movement between thelocking device and the bone pin, such that also relative moment of thebone pin with respect to the connection device is prevented.

In order to achieve an efficient locking of the bone pin, the lockingdevice according to a preferred embodiment comprises an engaging surfacefor engaging the bone pin, wherein the engaging surface is movabletowards and from said bone pin between an unlocked position, wherein thebone pin is movable with respect to the engaging surface, and a lockingposition, wherein the engaging surface engages the bone pin for lockingsaid bone pin with respect to the connection device by clamping. Thestep of locking the bone pin in the method according to the inventiontherefore preferably comprises engaging the bone pin with an engagingsurface of the locking device for clamping said bone pin. The engagementsurface is preferably moveable radially inwardly towards thelongitudinal axis of the bone pin.

It may be possible that the engagement surface is only movable from theunlocked position to the locked position, such that the bone pin can nolonger be loosened after locking with the locking device, preferablywith (but not restricted to) plastically deforming either of thecomponents, preferably the locking device. It is however preferred ifthe engaging surface is also movable from the locked to the unlockedposition, such that the bone pins can be loosened if needed.

The engaging surface may for instance be formed on movable or deformableparts of the locking device, such as tongues, which are movable towardsand preferably also from the bone pin for locking the bone pin.

Preferably, the locking device has an inner diameter substantiallycorresponding to the diameter of the bone pin. In this embodiment, thelocking device can only be placed in the opening after the removal ofthe guiding tube, as the guiding tube would not fit in the lockingdevice. Providing a locking device having an inner diametercorresponding to the outer diameter of the bone pin allows a goodlocking action, as for instance the engagement surface only needs to bedisplaced over a little distance to obtain a good clamping action.

As an alternative, the locking device has an inner diametersubstantially corresponding to the outer diameter of the guiding tube inthe unlocked position. This allows the locking device to be already inplace in the opening when the guiding tube is guided in the opening. Thelocking device may then have a guiding function for guiding the guidingtube. When the guiding tube is removed after insertion of the pin in thebone, the engagement surface is moved towards the bone, thereby bridgingthe wall thickness of the then removed guiding tube, to clamp the bonepin.

In order to be able to efficiently move the engaging surface to thelocked position, the opening of the connection device preferably has atapering diameter, seen along the longitudinal axis of the opening, formoving the engaging surface between the positions, upon longitudinalmovement of the locking device with respect to the connection device.The step of locking the bone pin in the method according to theinvention then preferably comprises moving the locking device along thelongitudinal axis of the opening of the connection device for urging theengaging surface onto the bone pin. The tapering diameter, or at leastvarying diameter, of the opening then serves as a guiding surface forguiding the engagement surface towards the bone pin for engagement. Tofurther improve the movement of the engaging surface, the locking devicepreferably comprises a correspondingly shaped tapering outer diameter.

As an alternative, it is also possible that only the locking device hasa varying outer diameter, for instance a wedge shape, which urges theengaging surface onto the bone pin upon movement of the locking deviceinto the opening.

According to a further preferred embodiment, the locking devicecomprises a deformable element arranged to deform in the locked positionfor engaging the bone pin. The deformable element may for instance bemanufactured from a resilient material such as rubber or flexibleplastic.

The locking device may be formed as a single unit. This reduces thenumber of parts. It is however also possible that the locking devicecomprises an engaging element provided with at least one engagingsurface and a separate driving element arranged to move the engagingelement along the longitudinal axis of the opening for moving theengaging surface from the unlocked to the locked position. It is forinstance possible that the driving element is removed from the openingafter locking the bone pin with the engaging element. This preventsaccidental loosening of the bone pin.

It is however preferred when the engagement element is arranged to bemoved to the locked position upon movement in the opening along thelongitudinal axis as explained above, that the engaging elementcomprises at least one second engaging surface at a distance from thefirst engaging surface, seen along the longitudinal axis of the opening.This allows clamping at two locations of the bone pin, thereby improvingthe locking action. The driving element is then preferably provided withan opening for receiving the engaging element and wherein the opening ofthe driving element has a tapering diameter, seen along the longitudinalaxis of the opening, for moving the second engaging surface between theunlocked and locked position upon longitudinal movement of the drivingelement with respect to the engaging element. Also the engaging elementand the driving element are then provided with a cooperating guidingsurfaces for urging the engaging surface towards the bone pin. As said,this improves the locking action.

According to a further preferred embodiment, the opening comprises, seenalong the longitudinal axis of the opening, a first section having afirst diameter and a second section having a second diametercorresponding to the outer diameter of the guiding tube, wherein thefirst diameter is larger than the second diameter. The change indiameter can be used to move the engaging surface towards the bone pinas mentioned above. The broader section moreover allows receipt of thelocking device. To efficiently move the engaging surface as mentionedabove, it is further preferred if the opening comprises a taperingsection extending between the first and the second sections in which thediameter tapers from the first diameter towards the second diameter. Itmay be possible that the second section has a limited length, such thatthe tapering section extends until the end, wherein diameter at the endcorresponds to the second diameter.

According to a further preferred embodiment, the opening of theconnection device and the locking device are provided with cooperatingconnecting means for interconnecting the locking device and theconnection device. This improves the locking action. Several types ofconnecting means may be used. It is for instance possible to use abayonet connection between the locking device and the connection devicehaving a resilient lip engaging in a correspondingly shaped recess orgroove. For instance in the case a deformable part is used, it ispreferred if the opening is provided with a recess, preferably a groove,for receiving the deformable element for locking the connection deviceand the locking device.

Efficient locking, while allowing easy manipulation, is however obtainedif the locking device and the connection device are provided withcooperating threading.

In case a driving element is used, it is preferred if the drivingelement and the opening of the connection device are provided withcooperating connecting means. This then locks the driving element withrespect to the connection device, while the locking element and thedriving element are further preferably also provided with cooperatingconnecting means.

In order to provide sufficient room for the connecting means, it ispreferred if the connecting means are provided in the first, broadersection of the opening.

As mentioned above, it is possible that the locking device is arrangedto receive and guide the guiding tube. The locking device thereto has asuitable inner diameter. It is however also possible to use a separateguiding element, such that the locking device is dedicated to lock thebone pin. The inner diameter of the locking device may then correspondto the outer diameter of the bone pin as mentioned above. Therefore, afurther preferred embodiment of the system further comprises a guidingelement for guiding the guiding tube, wherein the guiding element isarranged to be received in the opening of the connection device, whereinthe guiding element has an outer diameter corresponding to the diameterof the opening and wherein the guiding element has an inner diametercorresponding to the outer diameter of the guiding tube, wherein theguiding element and the guiding tube are removable from the combinationof the bone pin and the connection device. The method according to theinvention then preferably further comprises the step of inserting aguiding element in the opening of the connection device and arrangingthe guiding tube in said guiding element.

After proper guidance of the guiding tube, which in turns guides thebone pin to the bone, the guiding tube and the guiding element areremoved. Preferably, the guiding element is removed prior to locking thebone pin. Also the guiding element preferably has an annular body. Theouter diameter thereof preferably corresponds to the diameter of theopening, more preferably the annular body has an outer diametercorresponding to the diameter of the first section of the opening. Theguiding element is then placed in the first section of the opening andserves to bridge the distance between the inner wall of the opening andthe guiding tube.

In order to at least temporary fix the guiding element to the connectiondevice to allow a stable guidance of the guiding tube, the guidingelement is preferably provided with corresponding connecting means forinterconnecting the guiding element and the connection device. The sameconnecting means as used for connecting the locking device in theopening are preferably used.

According to a further preferred embodiment wherein a separate drivingelement is used, said driving element is formed as the guiding element.This reduces the number of parts.

The system according to the invention is in particular useful forconnecting a connection device to a bone with two parallel bone pins. Afurther preferred embodiment of the system according to inventiontherefore further comprises a second locking device, wherein theconnection device comprises a second opening for receiving a second bonepin, wherein the longitudinal axes of the first and the second openingsare substantially parallel and wherein the second locking device isarranged to lock the second bone pin after removal of a guiding tubefrom the second opening. The openings hereby define at least one of thetrajectories of the bone pins to be inserted into the bone.

The invention thus further relates to a method for connecting aconnection device to the bone with two parallel bone pins, comprisingthe step of connecting a connection device to the bone with a first bonepin and connecting the connection device to the bone with a second bonepin according to the method according to the invention. Using twoparallel bone pins allows adjustment of distance of the connectiondevice with respect to the patient, in particular when the lockingdevice also allows loosening of the bone pins after locking said bonepin.

At least the second bone pin is connected in the above described manner,wherein the opening is used as drilling guide. After placement of afirst bone pin at the most appropriate preferred anatomical position,the locations of additional bone pins is (to a certain extend)determined as they are all to be connected to the same external device.To facilitate guiding of the subsequent bone pins for fixation to anexternal device to the optimal anatomical bone pin positioning there isan advantage to use the for each application specifically designedconnection device as bone pin positioning guide or drilling guide. Inthis way the optimal anatomical position of the bone pin is directlyrelated to an optimal connection to the device and with that themechanical positioning of the device. Moreover, the optimal anatomicalpositions can be found intuitively by the guidance of the connectingdevice.

The first pin may also be fixed using the system and method according toinvention. It is however also possible that the step of connecting aconnection device to the bone with a first bone pin comprises:

-   -   inserting the bone pin into the bone using a guiding tube;    -   removing said guiding tube from the inserted bone pin;    -   arranging the connection device onto said inserted bone pin;    -   locking the bone pin with respect to the connection device with        a locking device,        wherein the method further comprises subsequently connecting the        second bone pin according to the method according to the        invention. As the position of the connection device with respect        to the patient is then fixed, it is an advantage that the        slidable guiding tube is adjustable in depth to allow efficient        protection of the surrounding tissue upon insertion of the        second bone pin.

The invention further relates to an external orthopaedic device arrangedto be connected between a first bone part and a second bone part,wherein the orthopaedic device comprises a first connection deviceaccording to the invention and a second connection device, preferablyalso according to the invention. This orthopaedic device can beconnected efficiently to the patient as discussed above.

For each application this connecting device will be specifically shapedto guide the bone pins of the second connecting device intuitively tothe preferred anatomical bone pin position and to provide optimalpositioning of the second connecting device regarding mechanicalcharacteristics of the entire configuration.

The invention further relates to an external orthopaedic device in theform of an external distractor arranged to gradually enlarge thedistance between a first bone part and a second bone part, wherein thedistractor comprises a first connection device, preferably as definedabove, and a second connection device, preferably also as defined above,wherein the first connection device is arranged to be connected to thefirst bone part with at least one first bone pin and wherein the secondconnection device is arranged to be connected to the second bone partwith at least one second bone pin, wherein the first and secondconnection devices are interconnected via at least a distraction device,the distraction device having an adjustable length for adjusting thedistance between the first and the second connection devices along anadjustment axis.

The distractor device preferable comprises a first part and a secondpart which are movable with respect to each other along the adjustmentaxis. The parts may for instance be provided with cooperating threadingto allow the adjustment of the length. The distractor device ispreferably arranged to adjust the distance between the bone pins whilemaintaining the structural integrity of the distractor. The distance canthus be adjusted while transferring loads between the first and secondbone parts.

The invention therefore also relates to a method for connecting anexternal distractor between at least two bone parts of a patient,comprising the steps of:

-   -   providing an external distractor according to the invention;    -   connecting the first connection device to the first bone part        with at least one bone pin; and    -   connecting the second connection device to the second bone part        with at least one bone pin.

In particular when using the connection system according to theinvention, the distractor can efficiently be connected to the patient.It is however noted that the invention is not necessarily limited to adistractor having connection devices according to invention. Addition ofother connection devices, such as connection blocks which are known assuch, may also be used.

In order to prevent further wear and tear of the damaged articulatingsurfaces and to potentially stimulate the regenerating capability of thejoint, it is preferred if the distractor, in particular the distractordevice thereof, comprises resilient means which are arranged forallowing resilient movement along the adjustment axis between theconnection devices. The resilient means, for instance in the form of aspring or similar device, then allows small displacements along theadjustment axis.

Although it is possible that the distractor device directly couples thetwo connection devices, it is preferred if the external distractorfurther comprises an interconnecting system extending between the firstand second connection devices, wherein the interconnecting system ismovable between an unlocked position, wherein the connection devices aremovable with respect to each other, and a locked position, wherein themutual positions of the connection devices are fixed. Theinterconnecting system allows the connection devices to be moved withrespect to each other which is in particular useful when connecting thedistractor to the patient.

The interconnecting system may for instance comprises at least onelockable hinge, preferably two at either side connected to theconnection devices. It is preferred that the interconnecting system isconnected to the first and second connection devices with two respectivelockable ball joints. This allows the connection devices to beefficiently moved with respect to each other.

A preferred method according the invention therefore preferably furthercomprises the steps of:

-   -   providing the interconnecting system in the unlocked position;    -   aligning at least one of the connection devices along a        predetermined axis with respect to a bone part; and    -   moving the interconnecting system to the locked position for        fixing the mutual positions of the connection devices after        alignment.

Preferably, the interconnecting system is moved to the locked positionafter fixation of the bone pins.

According to a further preferred embodiment, the distraction device isarranged in one of the connection devices, preferably integrally,wherein the interconnecting system extends between the distractiondevice and the other connection device. More preferably, the ball jointis formed as a part of the distractor device. The distraction device ishereby coupled between a connection device, and the interconnectingdevice. Although the distraction device may be formed integrally, it isalso possible that the distraction device is insofar arranged in one ofthe connection devices that the minimal distance between the opening inthe connection device and the adjustment axis of the distraction deviceis movable and can be fixed. The location of the opening in theconnection device may for instance be adjustable along the adjustmentaxis of the distraction device to allow adjusting the length of thedistractor upon connecting the distractor to the patient.

To allow efficient distraction, in particular of a joint, it isimportant that the distraction device is correctly aligned with the boneparts. It is in particular preferred if the adjustment axis is alignedwith at least one of the longitudinal axes of the bone parts. The stepof aligning therefore preferably comprises aligning the longitudinalaxis of a bone to be substantially parallel to the adjustment axis ofthe distraction device. This alignment is more easy to perform if thedistraction device is part of one of the connection devices as mentionedabove, although this is not strictly necessary.

In order to allow connection of the connection device to a bone withoutdamaging fragile soft tissue (at the anatomically preferred locations),while still allowing axial displacement parallel with the longitudinalaxis of the bone (for optimal mechanical performance of theconfiguration), for instance the tibia, according to a further preferredembodiment the connection device is arranged to receive the bone pin ata certain distance from the adjustment axis.

In order to transduce loads over the joint via the distraction device,correction in alignment is required to ensure optimal unloading of thejoint. A certain off-set of the bone pin connection to the axis of thedevice as well as preferably a certain curvature in the device as willbe explained below to obtain optimal anatomical bone pin locationsrelative to optimal mechanical positioning of the external device willbe needed.

According to a further preferred embodiment, at least one of theconnection devices is arranged to be connected to the bone part with twosubstantially parallel bone pins. This improves the stability of thesystem, while the distance of the connection device and the patient isstill adjustable as explained above.

At least one of the steps of connecting a connection device to therespective bone part according to the invention then comprisesconnecting the connection device to two substantially parallel bonepins. Preferably both connection devices are connected to the bone withtwo parallel bone pins.

The connection devices thereto preferably comprise two openings forreceiving two bone pins. The step of aligning then preferably comprisesaligning the connection device such that the openings in the connectiondevice are arranged along an axis substantially parallel to thelongitudinal axis of the respective bone part. This allows efficientalignment, wherein the openings in the connection devices are used as areference for alignment.

It is then preferred if a connection device is provided with twoopenings for receiving the two bone pins, wherein the openings in theconnection device are arranged along an axis at a distance from thepivot point of the ball joint. This creates an offset between the pivotpoint of the ball joint and the openings through which the bone pins areto extend. This offset allows an improved connection to the bone, at thepreferred anatomical positions of the bone pins, preventing potentialdamage to sensible surrounding tissues. This offset may be specific forspecific devices for specific joint bones.

For the connection device provided with the distraction device, it ispreferred that when the connection device is provided with two openingsfor receiving the two bone pins, the openings in the connection deviceare arranged along an axis substantially parallel to the adjustment axisand such that the two bone pins extend substantially perpendicularly tothe adjustment axis. The openings of the connection device can then beused to correctly align the adjustment axis with a predetermined axis ofthe bone, preferably the longitudinal axis of the bone. It is againpreferred if an offset is created between the adjustment axis and anaxis onto which the openings in the connection device extend. Theopenings in the connection device are therefore preferably arrangedalong an axis at a distance from the adjustment axis.

In particular for distracting a knee joint, it is preferred if oneconnection device is arranged to receive its bone pins at a distance ina first direction from the adjustment axis or the pivot point, whereinthe second connection device is arranged to receive its bone pins at adistance in a second direction from the adjustment axis or the pivotpoint, the second direction being substantially opposite to the firstdirection. This protects sensible tissue when inserting the bone pins inaccordance with the openings provided at an offset as explained above.Moreover, it provides intuitive positioning of the bone pins at thepreferred anatomical locations, guided by the openings in the connectiondevice.

In order to further adapt to the curvature of the patient, it ispreferred if the connection device comprises a patient facing surfaceand an outer surface, wherein an opening extends between the patientfacing surface and the outer surface, wherein at least the patientfacing surface of the connection device has a curved cross-section, seenin a plane perpendicular to the axis trough the openings. The patientfacing surface is then preferably curved in accordance with thecurvature of the patient. This provides further intuitive positioning ofthe bone pins at the preferred anatomical locations, guided by theopenings in the connection device.

The distractor is particularly suitable to be used to distract the kneejoint. The invention thus also relates to a method for connecting anexternal distractor between the tibia and the femur, wherein one of theconnection devices is connected to the tibia and the other connectiondevice is connected to the femur.

When setting joint distraction to the distraction device, only anincreasing joint space width is aimed for, while further jointconfiguration remains intact. To do so, the distraction direction needsto be orthogonal to both joint surfaces. In case of the knee this meansperpendicular to the tibial surface and in the axial direction of thetibia. Specifically to the knee joint, the femoral joint side has aconvex, spherical like, surface, while the tibial joint side has a moreflattened concave corresponding surface. A direction of distractionorthogonal to both joint sides can be achieved, independent from flexionangle of the joint, by choosing the direction orthogonal to the leastspherical surface, or orthogonal to the most flattened surface.

As the connection of the bone pins in the femur is more critical interms of surrounding tissue which may be damaged, it is preferred if thefemur is connected to its connection device prior to connecting thetibia to its connection device.

It is hereby possible that the first pin is inserted into the femurusing a guiding tube, to subsequently connect the connection deviceaccording to the invention. A second bone pin can then be inserted intothe bone using the connection device as drill guide after properalignment of the connection device, in particular along the longitudinalaxis of the bone.

According to a further preferred embodiment, the step of aligningcomprises aligning the adjustment axis of the distraction device in theconnection device to be substantially parallel to the longitudinal axisof the tibia in the coronal plane and preferably the sagittal planesubstantially perpendicular to the tibial plateau. This provides anefficient distraction of the knee joint.

It is hereby noted that it is in particular important that thelongitudinal axis of the tibia is aligned with the adjustment axis. Itmay for instance be possible that the patient is not capable ofcompletely extending the knee, such that the alignment axis is notproperly aligned with the longitudinal axis of the femur, such that theconnection device on the femur is not aligned with the longitudinal axisof the tibia. The interconnection system then still allows properalignment of the connection device on the tibia, such that theadjustment axis is parallel to the longitudinal axis of the tibia asexplained above.

It is noted that the term aligned as used herein is to be understoodthat the axes to be aligned are substantially parallel, that is within±10 degrees with respect to each other.

It is hereby preferred if each of the connection devices is providedwith two openings for receiving the two bone pins, wherein theconnection devices are aligned such that the openings in the connectiondevice are arranged along axes substantially parallel to thelongitudinal axes of the respective bones and such that the two bonepins extend substantially perpendicularly to the longitudinal axes ofthe respective bones. In order to prevent damage to tissue as alreadymentioned above, it is then preferred if the step of aligning theconnection devices further comprises aligning the adjustment axis and/orthe pivot points of the ball joints substantially on the coronal plane,and:

-   -   orienting the openings of the connection devices to be connected        to the femur in a posterior position; and/or    -   orienting the openings of the connection devices to be connected        to the tibia in anterior position.

The distractor as explained may be used as an unilateral distractor. Itis however preferred to use the system as a bilateral system forapplication of knee joint distraction. The invention thus also relatesto a method for connecting an external distractor system between atleast two bone parts of a patient, comprising the steps of connecting afirst external distractor according to the invention at a first side ofthe bone parts and connecting a second external distractor according toinvention at a second side, opposite the first side of the bone parts.It is hereby preferred if the first and second external distractors arearranged substantially on the similar coronal plane on either side ofthe knee.

The present invention is further illustrated by the following Figures,which show a preferred embodiment of the device and method according tothe invention, and are not intended to limit the scope of the inventionin any way, wherein:

FIGS. 1a-d schematically show a system and method for connecting aconnection device to a bone;

FIGS. 2a-d schematically show a variant of the system of FIG. 1;

FIGS. 3a and b schematically show a variant of fixing a bone pin to aconnection device;

FIG. 4 shows a variant of a connection device having two openings;

FIG. 5 shows a distractor according to the invention;

FIGS. 6a-c shows a first connection device of the distractor of FIG. 5in perspective, top view and side view respectively;

FIGS. 7a-d shows a second connection device with distraction mechanismin perspective, top view in two positions and in side view respectively;

FIG. 8 shows the positional relationship of the bone pins of the twoconnection devices in side view;

FIGS. 9 and 10 show a joint knee and the femur and tibia in crosssection indicating the bone pin positions; and

FIGS. 11a-c show a bilateral distraction system according to theinvention.

In FIGS. 1a-d the steps for connecting a connection device 1 in the formof a connection block to a bone 100 is shown. The connection block 1 isthereto provided with an opening 11 which extends between a firstsurface 12, which faces the patient 101, and a second surface 13 whichfaces away from the patient 101. The opening 11 has a section 11 atowards the second surface 13 which is provided with threading 14.Towards the patient facing surface 12, the opening 11 is provided with atapering section 11 b wherein the diameter of the opening 11 becomessmaller in the direction of the patient 101, seen along a longitudinalaxis A of the opening 11.

Inserted into the opening is a locking device 2 which has asubstantially annular shape and is shaped to fit inside the opening 11.The locking device 2 has a flange 21 at one side and deformable tongues22 at the other side and a body 23 provided there between. The body 23is provided with threading 24 for cooperation with the threading 14 ofthe opening. The outer diameter of the body 23 of the locking device 2thereby corresponds to the diameter of the first section 11 a of theopening 11. The length of the body 23 provided with the threading 24preferably corresponds to the length of the first second 11 a of theopening 11, seen along the longitudinal axis A.

The threading 14, 24 fixes the relative position of the locking device 2and the connection device 1, which position can be adjusted by rotatingthe locking device 2. In the position as show in FIG. 1a , the lowersurface of the flange 21 extends at a distance from the surface 13, suchthat further movement of the locking device 2 in a direction indicatedwith I in FIG. 1a is possible, as will be explained in greater detailbelow. In the situation as shown in FIG. 1a , the tongues 22 of thelocking device 2 only partially extend in the tapering section 11 b ofthe opening 11.

The inner diameter of the locking device 2, including the diameter atthe location of the tongues 22, corresponds to the outer diameter d1 ofa guiding cannula 3. This limits relative movement of the locking device2, which also serves as a guiding device for guiding the cannula 3, in adirection along the longitudinal axis A. The guiding cannula 3 isarranged to guide a bone pin 4 from the connection device 1 to the bone100, see FIG. 1b . In inserted situation as shown in FIG. 1b , thecannula 3 is thereto slidable along the longitudinal axis A with respectto the locking device 2 and thereby with respect to the connectiondevice 2. A flange 32 is provided to allow efficient adjustment of thedepth of the cannula 3. This allows efficiently guiding a bone pin 4 tothe bone 100, irrespective of the distance between the connection device1 and the bone 100. When the cannula 3 is advanced sufficiently far suchthat a distal end 31 abuts the bone 100, the bone screw 4 can beinserted into the cannula 3, schematically indicated with the arrow inFIG. 1b . The inner diameter of the cannula 3 thereto corresponds to theouter diameter of the bone pin 4 such that relative movement of the bonepin 4 in the cannula 3 is again restricted to movement along thelongitudinal axis A. The movement of the bone pin 4 with respect to theconnection device 1 is therefore also fixed.

In a next step, see FIG. 1c , the bone pin 4 can be fixed to the bone100. In this example, self-tapping bone screws 4 are used, such that thebone pins 4 are inserted into the bone 100 by rotating the bone pin 4inside the cannula 3. The cannula 3 thereby prevents damage to thesurrounding tissue of the patient 3. Other bone pins 4 can however beused.

After fixation of the bone pin 4 to the bone 100, the cannula 3 can bewithdrawn from the combination of the bone pin 4, the locking device 2and the connection device 1. This movement is indicated with the arrowin FIG. 1c . As the inner diameter of the locking device 2 correspondsto the outer diameter of the cannula 3, which is larger than the outerdiameter of the bone pin 4, the bone pin 4 is held in the locking device2 with play. Therefore, in order to lock the bone pin 4 with respect tothe locking device 2 and thereby with respect to the connection device1, the locking device 2 is rotated, thereby moving the locking device 2along the longitudinal axis A, see arrow in FIG. 1d , in the opening 11.The outer surfaces of the tongues 22 will thereby engage the innersurface of the tapering section 11 b, urging the tongues 22 radiallyinwardly, i.e. towards to the longitudinal axis and thereby towards thebone pin 4. The inner surface of the deformable tongues 22 thereby actas engaging surfaces which are arranged to engage the bone pin 4,thereby locking the bone pin 4 with respect the locking device 2 andthereby the connection device 1. In the locked position as shown in FIG.1d , the lower surface of the flange 21 of the locking device 2 abutsthe upper surface 13 of the connection device 1, which is in thisexample provided with a correspondingly shaped recess to receive theflange 21 in a countersunk manner.

In this situation, the bone pin 4 is firmly locked with respect to theconnection device 1. It will be appreciated, as will be explained ingreater detail below, that the bone pin 4 can simply be unlocked byrotating the locking device 2, thereby loosening the tongues 22 suchthat the locking device 2 is again movable with respect to the bone pin4.

In the example shown in FIGS. 1a-d , the locking device 2 serves to lockthe bone pin 4 and to guide the cannula 3. It is however also possibleto use a separate guiding device to guide the cannula 3. Moreover, inthe above example, the relative position of the locking device 2 and theconnection device 1 is fixed using threading 14, 24. Other means canhowever be used as will also be shown with reference to FIGS. 2a-d

The connection device 1 as shown in FIGS. 2a-d is similar to theconnection device 1 as shown in FIGS. 1a-d and is again provided with anopening 11. The diameter of this opening 11 is again larger than theouter diameter d1 of the cannula 3, such that a guiding device 5 is usedto limit the relative movement between the cannula 3 and the connectiondevice 1 along the longitudinal axis A, see FIG. 2b . The guiding device5 again has a annular shape and has an inner diameter corresponding tothe outer diameter d1 of the cannula 3. This allows efficient adjustmentof the depth of the cannula 3 with respect to the connection device 1 asindicated with double arrow in FIG. 1b . Note that this is differentfrom the locking device 2 as used in FIGS. 1a -d.

Instead of threading, the guiding device 5 is provided with a deformablepart 51 which locks into the opening 11 upon inserting the part 51. Thedeformable part 51 thereby exerts a clamping action of the inner surfaceof the opening 11, thereby retaining the guiding device 5 in the opening11 by friction. The guiding device 5 is further provided with a flange52 for easy manipulation of the guiding device 5.

After insertion of the bone pin 4, see FIG. 2c , the combination of theguiding device 5 and the cannula 3 can be removed from the combinationof the bone pin 4 and the connection device 1, see arrow FIG. 2d . Asthe bone pin 4 is firmly attached to the bone, the combination can bewithdrawn by pulling sufficiently hard to overcome the friction of thedeformable part 51 of the guiding device 5. The cannula 3 and theguiding device 5 can hereby be removed in unison.

Although a locking device similar to the locking device as shown inFIGS. 1a-d can be used to lock the bone pin 4 with respect to theconnection device 1, for instance by providing corresponding threading,it is also possible to use a locking mechanism formed of two separateparts, as is shown in FIGS. 3a and 3 b.

The locking mechanism comprises a driving element 6 and a lockingelement 7, wherein the annularly shaped locking element 7 is providedwith sets of tongues 71, 72 at either side. Both sets of tongues 71, 72are arranged to move radially inwardly upon deformation, thereby lockingthe bone pin 4. The first set of tongues 71 at the lower side of thelocking element 7 are moved radially inwardly upon moving, or driving,the locking element 7 in a direction indicated with the arrow in FIG. 1a. The reduction of the diameter indicated with 19 in the opening 11 willthereby urge the tongues 71 towards the outer surface of the bone pin 4.A groove 11 c is provided near end of the opening 11 towards thepatient, wherein ribs 71 a of the tongues 71 can snap for locking therelative positions of the locking element 7 with respect to theconnection device 1. In this locked position, the tongues 71 exert afirm clamping action on the bone pin 4 at a location along thelongitudinal axis A indicated with the arrow C in FIG. 3b , therebypreventing movement of the bone pin 4.

To further improve the locking action, also to the tongues 72 providedon the upper side of the locking element 7 will be urged radiallyinwardly upon movement of the driving element 6 towards the lockingelement 7. More specifically, the annularly shaped driving element 6 isprovided with an opening 61 of which the lower section 64 has a taperingdiameter, wherein the diameter increases towards the lower side. Thetapering section 64 forms a guiding surface for urging the tongues 72inwardly, i.e. towards the bone pin 4, when the driving element 6 ismoved towards the locking element 7.

Also the tongues 72 can be provided with ribs 72 a which can be receivedin a correspondingly shaped groove 63 at the end of the guiding surface.This connects the driving element 6 to the locking element 7 and therebyto the connecting device 1. In the situation as show in FIG. 3b , thetongues 72 exert a clamping action on the bone pin 4 at a location alongthe longitudinal axis A indicated with B, at a distance from location C.This improves the locking action of the locking mechanism.

The locking system may but not necessarily make use of ribs (71 a/11 cand 72 a/63) and corresponding grooves at either side or at both sides,to fix the 7 into the connecting device 1 or the driving element 6 orboth.

The connection system as described above is particularly suitable toconnect a connection device to a bone with two parallel bone pins. Thisis explained with reference to FIG. 4. Although in this figure aconnection system is shown which corresponds to the system as shown inFIGS. 1a-d , it will be appreciated that the same applies to the systemas shown in FIGS. 2 and 3, or combinations thereof.

In FIG. 4, a connection device 1 is shown provided with two parallelopenings 11, into which bone pins 4 a and 4 b are inserted. In thisexample, bone pin 4 a was inserted first by using a separate cannula todrill the bone pin 4 a into the bone 100. After fixation of this bonepin 4 a, the connection device 1 was advanced over the proximal end 42of the pin 4 a and the pin 4 a was locked with respect to the connectiondevice 1 using a locking device 2 a. In order to ensure that a secondpin 4 b was inserted parallel to the first bone pin 4 a, the connectionmethod similar to the methods shown in FIGS. 1 and 2 was used to insertand connect the bone pin 4 b. A cannula is thereby used to guide thebone pin 4 b to the bone 100, the surface of which differs in terms ofheight from the surface of the first bone pin 4 a as shown in FIG. 4.

In this example however, a separate guiding device was used (similar tothe method of FIG. 2) to guide the cannula, although a locking device inone piece was used (similar to the locking device of FIG. 1). Moreover,the interconnection of the locking devices 2 a and 2 b (and the guidingdevices which are not shown) with the connection device 1 is obtainedwith corresponding threading, again similar to the embodiment of FIG. 1.The situation of the bone pin 4 b as shown in FIG. 4 thus corresponds tothe situation of FIGS. 2d and 3a : after guidance and insertion of thepin and prior to locking of the pin 4 b.

Using a connection device 1 having two parallel openings for receivingbone pins, ensures that after fixation of a first bone pin in the bone,a second bone pin will be inserted into the bone parallel to the firstbone pin. The guiding device and the cannula after all limit movement ofthe bone pin with respect to the connection device along thelongitudinal axis of the opening. The connecting element as such guidingthe second bone pin to a preferred anatomical position.

Providing parallel bone pins allows adjusting the distance between theconnection device 1 and the patient 101, of which the skin 101 a isschematically indicated in FIG. 4. In case of for instance a swelling,as schematically indicated around bone pin 4 b, the locking devices 2 aand 2 b may be loosened, in this example by rotating the locking devices2 a, 2 b, such that the connection device 1 is again movable withrespect to the bone pins 4 a, 4 b, schematically indicated with thedouble arrow in FIG. 4. After displacement of the connection device 1along the longitudinal axes of the bone pins, the locking devices 2 a, 2b can again be tightened to lock the bone pins 4 a, 4 b with respect tothe connection device 1.

In the following figures, an external orthopaedic device, in thisexample in the form of a distractor 110 is explained. The externaldistractor 110 of this example is arranged to distract, that isgradually enlarge, the joint space width of the knee joint. Thedistractor 110 is thereto provided with connection devices 1 a, 1 b toreceive and lock the pins 4 a, 4 b with locking devices 2. Connectiondevice 1 a is arranged to be connected to the tibia with two parallelbone pins 4 a, whereas connection device 1 b is arranged to be connectedto the femur using two parallel bone pins 4 b. It is noted that althoughit is preferred to use a connection system as shown in any of the FIGS.1-4 to connect the bone pins 4 a, 4 b to the respective bones, this isnot strictly necessary. Other suitable connection systems may be used.

The connection devices 1 a, 1 b are interconnected by an interconnectingsystem 120. The interconnection system 120 comprises a central tubularmember 123 of which both ends comprise receptacles 121 a,b arranged toreceive balls 140 a, b (see for instance FIGS. 6a and 7a ) of theconnection devices 1 a, b for forming ball joints. The receptacles 121a, b for the balls 140 a,b are arranged to receive the balls 140 a, b ina rotating manner in an unlocked position and to prevent any relativemovement of the balls 140 a, b with respect to their respectivereceptacles 121 a,b in a locked position. In the unlocked position, theconnection devices 1 a, 1 b are substantially free to rotate andangulate with respect to the central tubular member 123, while in thelocked position, the relative positions of the connections devices 1 a,1 b are fixed with screw 122.

With reference to FIGS. 6a-c , the connection device 1 b is providedwith two openings 11 which extend between a patient facing surface 12and an outer surface 13. Both openings 11 are oriented parallel withrespect to each other. The longitudinal axes A of the openings, and thusof the inserted bone pins 4 b, therefore also extend parallel. Asmentioned above, the connection device 1 b is provided with a ball 140 bto form a ball joint when inserted into the receptacle of theinterconnecting system 120. With specific reference to FIG. 6b , it canbe seen that the ball 140 b, in particular the centre 140 c thereof,extends at a distance d2 from an axis A3 extending though (the centresof) both openings 11. The axis A3 is perpendicular to the longitudinalaxes A of the openings. The distance d2 is in this example determined asthe minimal distance between the axis A3 and the pivot point 140 c. Asshown in FIG. 6c , this construction creates an offset d2 of thelongitudinal axes A of the openings 11 (and thereby of the bone pins 4b) with respect to the pivot point 140 c. FIG. 6c further illustratesthat the lower surface 12 of the connection device 1 b is curved(bended) towards the patient, seen in the direction from the pivot point140 c towards the openings 11 in the lower surface 12, enabling optimalintuitive guidance to anatomically preferred positions of the bone pinswith proper mechanical characteristics of the whole configuration ofdevice and bones.

The other connection device 1 a is discussed in greater detail withreference to FIGS. 7a-d . Also this connection device 1 a is providedwith two parallel openings 11 for receiving two parallel bone pins 4 a.The openings 11 again extend between a patient facing surface 12 and anouter surface 13. Also this connection device 1 a is provided with aball 140 a to form a ball joint in combination with the receptacle 121 aof the connecting system 120.

The connection device 1 a is however further provided with a distractionmechanism, generally indicated with 130. The distraction mechanismcomprises means to adjust the distance between the bone pins 4 a and 4 bof the two connection devices 1 a, 1 b. More specifically, thedistraction mechanism is arranged to gradually increase the distancebetween the pivot point 140 c of the ball 140 a and the openings 11 forthe bone pins 4 a. This is achieved by cooperating threading provided onthe support 131 of the ball 140 a and rotatable ring 132 at the end of atubular base body 134 of the connection device 1 a. Rotation of the ring132 will adjust the distance L1 between the base body 134 and the ball140 a, as is visible in FIGS. 7b and 7c . This allows adjusting thelength L1 along an adjustment axis A4. In this example, the adjustmentaxis A4 is defined to extend through the centre 140 c of the ball 140 aforming the pivot point of the ball joint.

It will be appreciated that the adjustment of the length L1 along theadjustment axis A4 can take place without loosening the tension orstructural integrity between the two connection devices 1 a, 1 b,thereby keeping the joint at the preferred relative distance. In orderto allow adjustment of the distance between the two sets of bone pins 4a, 4 b prior to use, the connection device 1 a comprises a body 19 whichis arranged slidable along the tubular body 134 in a direction L2.Movement of the body 19, which is provided with the openings 11, can belocked using the screw 19 a.

In order to still allow little displacement along the adjustment axis A4during use of the patient, the stem 133 of the ball 140 a is resilientlysupported, in this example using a spring, in the support 131 of theball 140 a. Support 131 and stem 133 are thus allowed to move, asindicated with the double arrow L3 along the adjustment axis A4.

Although the ball 140 a is allowed to move with respect to the openings11 for receiving the bone pins 4 a, due to the distraction mechanism 130or the sliding movement between the body 19 and the tubular body 134,the relative orientation of the openings 11 along an axis A3 with therespect to the adjustment axis A4 remains unchanged. The axis A3extending between the two centres of the openings 11 and perpendicularto the longitudinal axes A thereof extends at a distance d3 and parallelto the adjustment axis A4. The same offset d3 is also visible in FIG. 7d, wherein also a curved patient facing surface 12 is shown as option.

As is already clear from FIG. 5, the offset of the bone pins 4 b in theconnection device 1 b is opposite to the direction of the offset in theconnection device 1 a with the distraction mechanism 130. This relativeorientation is further shown in FIG. 8, which is a view of the system ofFIG. 1 along arrow VIII in FIG. 5.

In FIG. 8 it can be seen that the longitudinal axes Aa, Ab of the twosets of pins 4 a, 4 b extend under an angle α with respect to eachother. The offset d2, i.e. the distance between the adjustment axis A4(also the pivot point 140 c) and the axis A3 through the openings 11 ofthe connection device 1 b is in the opposite direction of the offset d3,i.e. the distance between the axis A3 through the openings 11 in theconnection device 1 a and the pivot point 140 c. It also shows thecurvature in this case in one of the connecting devices 1 b. Thisconfiguration allows an efficient placement of the distractor 110 on thepatient, with preferred anatomical location of bone pins, preventingdamage to or interference with critical tissues.

In case of the knee joint, placement of a distractor 110 on a patient101 is explained while referring to FIGS. 9 and 10. In a first step offixing the distractor 110 to the patient 101 to distract the knee joint101 b, a first bone pin 4 b is inserted into the femur 101 c with anorientation which is posterior (indicated with P in the cross section ofFIG. 9b seen along the transverse plane Tp1 of FIG. 9a ) with respect tothe coronal plane Cp. This prevents damage to and/or interference withsensible tissue. For the fixation of the first pin 4 b, a separatecannula may be used to connect the bone pin 4 b to the bone 101 c. Afterfixation of the first bone pin 4 b, a connection device 1 b of thedistractor 110 is connected to the bone pin 4 b. The connection device 1b is then aligned such that the axis A3 between the openings 11 isaligned to be substantially parallel to the longitudinal axis Af of thefemur 101 c. The connection device 1 b is then used as drill guide,preferably using the system as shown in FIGS. 1-4, to insert a secondbone pin 4 b parallel to the first bone pin 4 b at the location of thetransverse plane Tp2. Bone pins 4 b then extend parallel andperpendicular to the longitudinal axis Af of the femur 101 c.

As the interconnecting system 120 of the distractor 110 is in theunlocked position, the connection device 1 a provided with thedistraction mechanism 130 is freely movable with respect to the alreadyfixed connection device 1 b. As it is important that the adjustment axisA4 of the distraction mechanism 130 is parallel to the longitudinal axisAt of the tibia 101 d, (FIG. 10) the connection device 1 a is arrangedsuch that the adjustment axis A4 is parallel to said longitudinal axisAt of the tibia 101 d. This can be done by aligning the axis A3 throughthe openings 11 in the connection device 1 a to be parallel to thelongitudinal axis At of the tibia 101 d.

With reference to FIGS. 10a and 10b , the trajectories A of the bonepins 4 a are chosen to be anterior (indicated with Ant in the transversesection of FIG. 10b along plane Tp1 in FIG. 10a ) with respect to thecoronal plane Cp. This prevents damage to and/or disturbance of sensibletissue. It is hereby noted that the configuration of the distractor 110and more in particular the offsets d2 and d3 as shown in FIG. 8automatically forces the posterior placement of the bone pins 4 b in thefemur 101 c and the anterior placement of the bone pins 4 a in the tibia101 (intuitive guiding of optimal anatomical positions of bone pins bythe device). The bone pins 4 a are inserted into the bone 101 d usingthe openings 11 of the connection device 1 a as drill guides, preferablyusing the method as shown in FIGS. 1-4.

After correct fixation of the two connection devices 1 a and 1 b atpreferred distance from the bone/skin enabled by parallel pins), theinterconnection system 120 can be moved to the locked position, therebyfixing the relative positions of the connection devices 1 a, 1 b.

It is possible to use the distractor 110 as an unilateral distractor. Itis however also possible to use the distractor in a bilateralconfiguration. For that case, a second distractor having a configurationwhich is mirror symmetrical with respect to the sagittal plane Sg (seeFIGS. 9B and 10 b) is connected to the patient. The orientation of thebone pins 4 a, 4 b for the femur 101 c and tibia 101 d is indicated inphantom in FIGS. 9b and 10b . This configuration is shown in FIGS. 11a-c, wherein FIG. 11a shows a transverse section in the femur 101 c, FIG.11b shows a transverse section in the tibia 101 d and FIG. 11 is a sideview of the system.

The present invention is not limited to the embodiment shown, butextends also to other embodiments falling within the scope of theappended claims.

The invention claimed is:
 1. A system for connecting a connection deviceto a bone with a bone pin, wherein the connection device is providedwith an opening for receiving the bone pin, wherein the systemcomprises: said connection device; a guiding tube arranged to guide thebone pin from the connection device to the bone for connecting the bonepin to the bone, wherein the inner diameter of the guiding tubecorresponds to the outer diameter of the bone pin and wherein theguiding tube can be slidably received in the opening, the guiding tubebeing slidable with respect to the connection device along only an axiscolinear to a longitudinal axis of the opening; and a locking devicearranged to be received in the opening of the connection device andarranged to engage the bone pin for locking the bone pin with respect tothe connection device, wherein the system is arranged to guide theguiding tube and to prevent any movement of the guiding tube relative tothe opening of the connection device other than a sliding movement alongthe longitudinal axis, and wherein the guiding tube is movable withrespect to the connection device and bone pin such that the guiding tubeis removable from the combination of the bone pin and the connectiondevice and wherein the locking device is arranged to lock the bone pinafter removal of the guiding tube.
 2. The system according to claim 1,wherein the locking device has an annular body having an outer diametercorresponding to the diameter of the opening of the connection deviceand an inner diameter suitable for engaging the bone pin.
 3. The systemaccording to claim 1, wherein the locking device comprises an engagingsurface for engaging the bone pin, wherein the engaging surface ismovable towards and from said bone pin between an unlocked position,wherein the bone pin is movable with respect to the engaging surface,and a locking position, wherein the engaging surface engages the bonepin for locking said bone pin with respect to the connection device byclamping.
 4. The system according to claim 3, wherein the locking devicehas an inner diameter substantially corresponding to the diameter of thebone pin.
 5. The system according to claim 3, wherein the locking devicehas an inner diameter substantially corresponding to the outer diameterof the guiding tube in the unlocked position.
 6. The system according toclaim 3, wherein the opening of the connection device has a taperingdiameter, seen along the longitudinal axis of the opening, for movingthe engaging surface between the positions upon longitudinal movement ofthe locking device with respect to the connection device.
 7. The systemaccording to claim 6, wherein the locking device comprises acorrespondingly shaped tapering outer diameter.
 8. The system accordingto claim 3, wherein the locking device comprises a deformable elementarranged to deform in the locked position for engaging the bone pin. 9.The system according to claim 8, wherein the opening is provided with arecess, preferably a groove, for receiving the deformable element forlocking the connection device and the locking device.
 10. The systemaccording to claim 3, wherein the locking device comprises an engagingelement provided with at least one engaging surface and a separatedriving element arranged to move the engaging element along thelongitudinal axis of the opening for moving the engaging surface fromthe unlocked to the locked position.
 11. The system according to claim10, wherein the engaging element comprises at least one second engagingsurface at a distance from the first engaging surface, seen along thelongitudinal axis of the opening, wherein the driving element isprovided with an opening for receiving the engaging element and whereinthe opening of the driving element has a tapering diameter, seen alongthe longitudinal axis of the opening, for moving the second engagingsurface between the an unlocked and locked position upon longitudinalmovement of the driving element with respect to the engaging element.12. The system according to claim 10, wherein the driving element andthe opening of the connection device are provided with cooperatingconnecting means.
 13. The system according to claim 1, wherein theopening comprises, seen along the longitudinal axis of the opening, afirst section having a first diameter and a second section having asecond diameter corresponding to the outer diameter of the guiding tube,wherein the first diameter is larger than the second diameter.
 14. Thesystem according to claim 13, wherein the opening comprises a taperingsection extending between the first and the second sections in which thediameter tapers from the first diameter towards the second diameter. 15.The system according to claim 13, wherein the connecting means areprovided in the first section of the opening.
 16. The system accordingto claim 13, wherein the guiding element has an annular body having anouter diameter corresponding to the diameter of the first section of theopening.
 17. The system according to claim 1, wherein the opening of theconnection device and the locking device are provided with cooperatingconnecting means for interconnecting the locking device and theconnection device.
 18. The system according to claim 17, wherein theopening and the locking device are provided with cooperating threading.19. The system according to claim 17, wherein the guiding element isprovided with corresponding connecting means for interconnecting theguiding element and the connection device.
 20. The system according toclaim 1, further comprising a guiding element for guiding the guidingtube and for preventing any movement of the guiding tube relative to theopening of the connection device other than a sliding movement along thelongitudinal axis, wherein the guiding element is arranged to bereceived in the opening of the connection device, wherein the guidingelement has an outer diameter corresponding to the diameter of theopening and wherein the guiding element has an inner diametercorresponding to the outer diameter of the guiding tube, wherein theguiding element and the guiding tube are removable from the combinationof the bone pin and the connection device.
 21. The system according toclaim 20, wherein the driving element is formed as the guiding element.22. The system according to claim 1, further comprising a second lockingdevice, wherein the connection device comprises a second opening forreceiving a second bone pin, wherein the longitudinal axes of the firstand the second openings are substantially parallel and wherein thesecond locking device is arranged to lock the second bone pin afterremoval of a guiding tube from the second opening.
 23. An externalorthopaedic device arranged to be connected between a first bone partand a second bone part, wherein the orthopaedic device comprises a firstconnection device as defined in claim 1 and a second connection device.24. A method for connecting a connection device to a bone with a systemaccording to claim 1, wherein the method comprises the steps of:providing a bone pin in said guiding tube in the opening of theconnection device; guiding the guiding tube to the bone by sliding saidguiding tube in the opening of the connection device with respect tosaid connection device, such that the guiding tube abuts the bone;inserting the bone pin into the bone; removing the guiding tube from thecombination of the bone pin and the connection device after insertion ofthe bone pin; and locking the bone pin with respect to the connectiondevice with said locking device after removal of the guiding tube. 25.The system according to claim 1, wherein the connection device isarranged to guide the guiding tube and to prevent any movement of theguiding tube relative to the opening of the connection device other thana sliding movement along the longitudinal axis.
 26. The system accordingto claim 1, wherein the locking device is arranged to guide the guidingtube and to prevent any movement of the guiding tube relative to theopening of the connection device other than a sliding movement along thelongitudinal axis.